It would be advantageous to provide an electronically scanned antenna (ESA) for applications that could not afford the cost and complexity of either a Transmit/Receive (T/R) module based active array or a ferrite-based phased array to achieve electronic beam scanning.
Electronic scanning of a radiation beam pattern is generally achieved with Transmit/Receive (T/R) module based active arrays or ferrite-based phased arrays The former can employ a T/R module at each radiator of the ESA. The T/R module may employ monolithic microwave integrated circuits (MMICs) to provide signal amplification and a multi-bit phase shifter to scan the radiation beam pattern. The latter employs passive ferrite phase shifters at each radiator to affect beam scan. Both techniques employ expensive components, expensive and complicated feeds and are difficult to assemble. Additionally, the bias electronics and associated beam steering computer are complex. Furthermore, ferrite phase shifter phased arrays are non-reciprocal antenna systems, i.e., transmit and receive antenna patterns are not the same. Ferrites are anisotropic, i.e., the phase shift of the energy in one direction is not replicated in the reverse direction. Ferrite phase shifter ESAs require large currents and complex bias electronics with customized timing to account for the hysteresis nature of most phase shifters.
Other methods to achieve beam steering are the PIN diode based Rotman lens and the voltage variable dielectric lens, employing barium strontium titanate (BST); a voltage variable dielectric material system. Both have either high current or high voltage (10 K volts) biasing requirements, as well as, high insertion loss, hence the radiation efficiency is poor.